Ok, so I’m riding through the forest last night, lost in my thoughts on the brake issue, between trying not to lose a lung.First thing I decide, is that it would be too hard for me to try to explain the brake proportion valve CLEARLY, when the good old Internet is filled with enough information to get Dislexidime lost forever. I don’t usually go looking for stuff, but this topic got me looking on the Net, and I was boggled at the information out there. So, with that in mind, I am attaching the link to the TILTON site, for HOW THE PROPORTIONING VALVE WORKS! And, more importantly, it shows the graph…which is very visual. This was going to be the tough part of the explanation…so I am taking the easy way out.

Now, I can talk about the valve from the drivers perspective, that I know, have lived with, and I think can comment from true experience.

My valve is and old DIRECT CONNECTION one, made by Kelsey -Hayes. It is an infinitely variable one, with a range from 100 to 1,000 PSI. It has small lines scribed on the screw shaft, which are kinda useless. I just put a reference mark on the valve mount, and, over time know how many turns to turn the knob, for a bias setting, which I note in my log. You can look at the graph in the Tilton link, and basically see what my screw type one looks like, in terms of the “knee point”. It sits by the passenger seat ( see picture). I have learned where to put it, based on going out on a straight stretch of road, and getting the brakes up to whatever I thought would be the appropriate temp, and see how the car feels under truly severe, race type braking situations. Don’t overheat the brakes, or you will not really get a reliable setting. The setting is the hard thing to describe, as, it is both determined, by what you may hear, and, more importantly, what you may FEEL in the seat of your pants. If you can hear the rear tires ripping rubber off…well…you have too much rear brake. You just want the car to be slowing down VERY HARD, and just have a “sense” as the weight is really finishing it’s transfer, that rear end ( read tires) are ALMOST getting to feel like you are on skippy bumps. That’s the hard part, and it just takes some testing, to get to that point, and maybe back it off just a tad more…depending on what you/the car, like.I have had the valve on my car for some 30 years now. Seems I never noted in my log book when I put it in, only reference the adjustments. So, with my master being the 15/16, the BMW 2002 4 piston steel calipers on the rear, and the front being the Brakeman 4 piston calipers, this is what I do with my brakes, via the proportioning valve. I am not going to get into the bore sizes, etc, as that is a discussion unto it’s self, and best left to those with good math skills, and able to build a balanced system, just using bore size matching alone, which still would not give you the ADJUSTABILITY, should you want it.In the case of my ride, I can adjust from the extreme of having severe rear lockup, to NO lockup at all, barring actually locking the whole system up, which I have never done. In my slaloming experience, one learns to be very smooth, and able to take the tires to incipient lockup, but no more.For driving on the street, which primarily means we have cold pads and rotors when we get onto the brakes, I have it set so that the front is doing most of the work. I have it set this way, should I have to really hit the brakes when cold, I will not get any rear lockup, and possibly cause me to want to come around. That being said, I have just enough rear bias, that when I enter a corner very fast, and I like to use trailing brake, the rear JUST feels like it is at the point of locking, and helps the car turn in a tad.

When I would road race, with sticky race slicks, I did not want the front doing most of the work, for all the reasons. I had more grip on the rear, so why put more heat into the front pads and rotors, at a disproportionate rate, by having HUGE weight transfer to the front. I would screw the knob IN, thus ALLOWING more pressure to the rear ( again, you must read the Tilton link, as it explains about the pressure!!!!). This would decrease the weight transfer, and make the rear work harder, which the car could tolerate. Now, there are a lot of factors going on here, main one being temperature. It took me a while to figure out the optimum amount to change to knob, as it took awhile for the pads/rotors to get to their equilibrium…KINDA. Obviously you keep introducing more heat, if you have undersized rotors, and or poor cooling, which can start to change things too. Balance..pun intended….becomes just a case of both testing, and knowing your car and driving style.

I had a problem to deal with also…pad choice. I could NOT get the same compound, from the same manufacturer. This gave a problem of have a relatively grippier pad at the front, which both caused the weight transfer to happen, and the lightly loaded rear to be not doing much. In my case , the difference in the coefficient of friction from front to rear, made for some interesting braking situations. Having the ability to fine tune things with the valve was a bonus, let alone a necessity for good PREDICTABLE braking.

And, what fuel load do you have? More weight over the rear, you can get away with more rear bias. This is really only a factor in a road race setting, where you are getting lighter in the rear, and want to back off the rear bias. That is where the TILTON LEVER type is likely better, you have 7 click stops.

As the so called DOT street legal race rubber has come along, the better grip has let me run with a bit more rear bias, and, this summer I am going to try dialing some more in. I will be the first to admit I am just not a hero when it comes to an over steering car. I have been very conservative about how much rear bias I have. I can really haul down INTO a corner, and as I have harped about before in regards to rear toe change, be able to get HARD on the brakes if I have to, and not worry about it either locking, or trying come around under heavy braking.

So, do you NEED a proportion valve…depends! Read the above again. Coming from my racing back ground, and a car(s) that were ALWAYS evolving, ever changing tires and grip……I NEEDED ONE..PERIOD!I have done so many types of events’, it was the only way to both stay competitive, and safe. I had drum brakes originally, and when I changed to the “green stuff” shoes, things started to go to hell, in terms of brake balance.We also now, and have for years, put on a hodge podge of different components, to do with the brake system, none of which were ever designed to be compatible.

My brake system uses all the stock line plumbing, except steel braided lines for the front and rear calipers. My shuttle valve is intact, as is the “brass” T at the fire wall.

So, botttom line for me, is that I have a complete range of adjustment for my brake balance, letting me maximize my decelerations, at a hell of a rate!!

Keith, excellent writeup. Thanks. I have one of those same K/H prop valves in the take-outs. I should take it apart and post some pictures of it (I'm not machining it in half though, because I told James he could have it for his car's new gross brake setup)

Now, with respect to the shuttle valve thing-a-ma-jig-block, who told us that the shuttle floated in the middle??? For all intents and purposes, the cutaway shows virtually no end-to-end free play in the floating shuttle component - it is more or less held in place with springs, implying that for any movement to occur, and presuming that only a single-sided pressure were presented to either of the two fluid connection, that single applied fluid pressure would have to exceed the seat force of the opposing spring to cause displacement of the shuttle.

Jeff - experiment time...

Pt 1) You have to measure the mechanical movement needed to trigger the switch (using your cutaway part). Shuttle position in natural position, shuttle displacement needed to trigger the electrical contact.

Pt 2) Using another (unmachined) sample assembly, you need to apply a fluid pressure to only one half of the assembly, monitoring the applied fluid pressure needed to trigger the electrical contact.

Pt 3) Repeat Pt 2 of the experiment for the other fluid circuit.

You don't really need to know Pt 1, but I certainly do enjoy being a TOTAL nerd.

(Jeff, One of those Auber Ins. pressure sensors would be ok to have right about now... I don't imagine that the pressure required to activate the electrical contact exceeds 150 psi, but it's hard to guess without quantifiable data. For what it's worth, one of those pressure sensors would make a slick fuel pressure sensor after using it to experiment (tell Dave he has to buy one for you in the name of Jeff's science project). After completing the experiment, you could connect one of those sensors straight into an MS box to data log fuel pressure if you so desired (you don't really need the gauge module, because those sensors are comensated internally). Higher pressure ones are available from Digikey etc...)

One thing I wanted to make sure was correct for those that might read this and not know is about the pressures in a sealed fluid system.

Byron510 wrote: However, as I understand it:

A 1” M/C cylinder bore with 100 lbs of pedal pressure traveling 1” distance in the bore will exert 100 lbs of line pressure (assuming a pedal ratio of 1:1 – which it isn’t, I know, but were are only talking theory here). This 100 lbs line pressure acting on a 4” front caliper bore will net 400 lbs of force but only travel .250” of distance, and inversely the same M/C will exert 50 lbs pressure on a ½” bore but travel twice the distance of the M/C (2” travel at the rear ½” cylinder. Someone correct me if I’m wrong here.So increasing the front caliper piston size (or the square area of all your pistons added together for multiple piston calipers) will decrease the amount of piston travel, however increase the pressure available.

It's my understanding, from my auto college training, which was years ago and may be foggy by now , that the pressure inside a closed fluid system that is unmodified is equal in all areas. This means, without the presence of any component modifying a pressure signal of the front or rear, that if there's 100 psi in the front caliper then there is also 100 psi in your rear wheel cylinders/calipers and in every nook and cranny of the lines. So the size of the cylinder or piston doesn't change the pressure within the given caliper or cylinder. The different pressure applied between the pad and rotor is then a product of line psi and piston inside surface area which would be the same front and rear if not modified by components. THEN the actually difference in braking power is the friction between the pad and rotor which is a product of pressure exert from the caliper piston and the metal material and brake pad material.

This may seem insignificant to understand, but it is a base principle that needs to be understood before moving on to devices that manipulate the pressure front and rear.

ALSO, just a little other detail to understanding line pressure. Even if, although not likely, the shuttle valve moved over half way and didn't fully close off one side, then theoretically both front and rear would STILL have the same line pressure. I'm not saying this as an actual scenario that might happen because if it were to overcome the spring pressure my guess is there would be a major failure and it would close one side completely. I'm just saying this to state that according to what I learned the ENTIRE circuit has the same pressure no matter how small the hole. This is the concept that allows 100 psi in such a small brake line translate into 100 psi in a relatively huge brake caliper piston.

And as always please correct me if I'm off on any of this, constructive criticism is always welcome )

"An intercooler...has never been, nor should ever be, considered icing on the cake. A proper intercooler is more cake."Corky Bell, Maximum Boost

heirfaus wrote:It's my understanding, from my auto college training, which was years ago and may be foggy by now , that the pressure inside a closed fluid system that is unmodified is equal in all areas. This means, without the presence of any component modifying a pressure signal of the front or rear, that if there's 100 psi in the front caliper then there is also 100 psi in your rear wheel cylinders/calipers and in every nook and cranny of the lines. So the size of the cylinder or piston doesn't change the pressure within the given caliper or cylinder. The different pressure applied between the pad and rotor is then a product of line psi and piston inside surface area which would be the same front and rear if not modified by components. THEN the actually difference in braking power is the friction between the pad and rotor which is a product of pressure exert from the caliper piston and the metal material and brake pad material.

This may seem insignificant to understand, but it is a base principle that needs to be understood before moving on to devices that manipulate the pressure front and rear.

I agree somewhat, but PSI stands for pounds per square inch. if your gauge says 100psi and the caliper has 2 square inches of surface area it will have 200psi of pressing force. I do think that the line pressure is equal plus or minus a few percent.

heirfaus wrote:ALSO, just a little other detail to understanding line pressure. Even if, although not likely, the shuttle valve moved over half way and didn't fully close off one side, then theoretically both front and rear would STILL have the same line pressure. I'm not saying this as an actual scenario that might happen because if it were to overcome the spring pressure my guess is there would be a major failure and it would close one side completely. I'm just saying this to state that according to what I learned the ENTIRE circuit has the same pressure no matter how small the hole. This is the concept that allows 100 psi in such a small brake line translate into 100 psi in a relatively huge brake caliper piston.

And as always please correct me if I'm off on any of this, constructive criticism is always welcome )

I don't think the shuttle valve does huge moves I just think that the shuttle valve and restricter bolted to the firewall behind the engine act as a team. Allowing the initial break pedal mashing to in-gauge the front brakes a little harder while restricting the rear brakes mechanically for micro seconds while the weight transfers. Then the pressures equal out and the brakes are balanced the way they where designed.

"People don't like it when shit doesn't match their rule of thumb." Sam

icehouse wrote:I agree somewhat, but PSI stands for pounds per square inch. if your gauge says 100psi and the caliper has 2 square inches of surface area it will have 200psi of pressing force. I do think that the line pressure is equal plus or minus a few percent.

Really......I am not sure but I don't think you can use that logic for calculating pressing force, I think that "PSI" is just a unit of measurement to determine complete system pressure. With that logic the 6 foot line would explode but the time you multiplied the PSI for every inch of the line. I think there is still 100 PSI of pressure at the caliper pad. People use bigger brakes to get more surface area of pad contact on the rotor, not to get higher pressing force. You would have to increase "system pressure" to do that. Am I close?? or am I clueless??

icehouse wrote:I agree somewhat, but PSI stands for pounds per square inch. if your gauge says 100psi and the caliper has 2 square inches of surface area it will have 200psi of pressing force. I do think that the line pressure is equal plus or minus a few percent.

Really......I am not sure but I don't think you can use that logic for calculating pressing force, I think that "PSI" is just a unit of measurement to determine complete system pressure. With that logic the 6 foot line would explode but the time you multiplied the PSI for every inch of the line. I think there is still 100 PSI of pressure at the caliper pad. People use bigger brakes to get more surface area of pad contact on the rotor, not to get higher pressing force. You would have to increase "system pressure" to do that. Am I close?? or am I clueless??

Nope, I'm going to have to lean towards the latter on this one More single piston area, or multiple pistons netting more area, increases pressure at the caliper pad. Why are you multiplying pressure in the line? The biggest advantage of bigger rotors is heat sink size and heat dissipation surface area, plus a longer leverage arm at the clamping point. The downside is then more rotating mass and more of that mass farther away from the axle meaning more rotational inertia to speed up and slow down. Consider a bicycle wheel - using your bare hand, would you rather try stopping it by squeezing the rim or the tiny axle?

Huh....ok, I see. but don't totally understand. It seems to me that it's still 100psi wherever it is in the system.....just because there is bigger area in the piston doesn't mean there is more pressure there, it's just more contact area....no? I was just trying to understand and learn a little something!!

Yes, the pressure in the closed system is 100 PSI (or whatever), and as the units imply, if your piston has 1 square inch of area it will exert 100 pounds of pressure on the pad, but if it's 2 square inches it will exert 200 pounds of pressure because you have 100 pounds acting on each square inch of area, but it will move half as far compared to the 1 square inch piston given the same amount of fluid.

Consider a hydraulic bottle jack that is capable of lifting many tons. You pump a lever (like a brake pedal) that is attached to a tiny little piston (like a master cylinder) which sends fluid into a comparatively large piston (like a brake caliper). Via the lever you exert an amount of force onto a piston of small surface area and move a certain amount of fluid. The lever provides a force proportional to the distance you push the lever down vs the distance the small piston moves, which is different because you're acting on a lever arm pivoting near the small piston. If you push the lever down one foot at the end and it moves the small piston down 1 inch at the other end you've multiplied your force and effectively have a 1:12 force multiplication. If you pushed down at 50 pounds the small piston sees 600 pounds. Let's say the small piston area is 1 square inch, so you've put 600 psi into the system moving X amount of fluid. Let's say the big piston is then something like 4" in diameter, so near 20 square inches. The large piston will thus exert a force of 600 * 20 = 12000 pounds. The volume of fluid in the small piston's cylinder is very small compared to the volume in the cylinder of the large piston, so you have to move a lot of fluid from the small cylinder to the big cylinder to get the big piston to move the same distance. Considering your brakes are adjusted (or self adjusting as newer ones are) this is okay because the pads are always right at the rotor surface and don't have to move far compared to how far the master cylinder moves. That's one reason why if your rear 510 stock drums are out of adjustment you will have a very soft pedal or no pedal at all. You're trying to move too much fluid before the shoes meet the drums.

Thanks, Matt. You explained it better than I could. My side point I was trying to make was that if, for example sake, the front brake lines were 1 inch in diameter and the rear brake lines were .1 inch in diameter, if all for calipers and rotors were the same then there would be the same braking force at all wheels.

Right?

This means that the shuttle valve should effect anything unless it fully closes off one side.

"An intercooler...has never been, nor should ever be, considered icing on the cake. A proper intercooler is more cake."Corky Bell, Maximum Boost

heirfaus wrote:Thanks, Matt. You explained it better than I could. My side point I was trying to make was that if, for example sake, the front brake lines were 1 inch in diameter and the rear brake lines were .1 inch in diameter, if all for calipers and rotors were the same then there would be the same braking force at all wheels.

Right?

This means that the shuttle valve should effect anything unless it fully closes off one side.

I don't think so, but my understanding of fluid mechanics if pretty limited. I know if you restrict the flow of fluid the pressure decreases (with an increase in fluid speed due to the restriction)...Bernoulli's principle I think. I'm not sure about after the fluid passes through the restriction, though...I guess there are ways to maintain the lower pressure even then. Maybe someone else here has studied this more.

thisismatt wrote:I don't think so, but my understanding of fluid mechanics if pretty limited. I know if you restrict the flow of fluid the pressure decreases (with an increase in fluid speed due to the restriction)...Bernoulli's principle I think. I'm not sure about after the fluid passes through the restriction, though...I guess there are ways to maintain the lower pressure even then. Maybe someone else here has studied this more.

It took me a while to think about this but then I realized that the pressure differential between the small and large diameters is only present in an open system where fluid is flowing. I had to look up Bernoulli's law as I hadn't ever official read it. In an open system the small line does have a higher pressure and the larger line has a lower pressure. I don't think this law applies here as we don't have flow in a closed system and even if we did the the rears would then have higher pressure in them. Right?

"An intercooler...has never been, nor should ever be, considered icing on the cake. A proper intercooler is more cake."Corky Bell, Maximum Boost